It's hard to imagine Christmas without images of a giant star in the night sky over Bethlehem, with one supernaturally bright beam pointing toward a stable.

For carolers, the key words are in "We Three Kings of Orient Are" where everyone sings: "Star of wonder, star of light, star with royal beauty bright. Westward leading, still proceeding, guide us to thy perfect light."

"The Christmas carols are surprisingly accurate when it comes to the details of what we know" from scripture, said New Testament scholar Colin Nicholl of Coleraine, Northern Ireland. "In many cases where they fill gaps in the biblical narratives, they end up including material that is pretty sound -- at least based on my research."

The problem is that this heavenly object simply does not behave like a star. Thus, in his new book "The Great Christ Comet: Revealing the True Star of Bethlehem," Nicholl blends material from history and science to argue that this phenomenon can best be explained by charting the path of what he calls "undeniably the single greatest comet in recorded history."

The language familiar to most readers is found in Matthew's Gospel, which states: "Now when Jesus was born in Bethlehem of Judaea in the days of Herod the king, behold, there came wise men from the east to Jerusalem, saying, 'Where is he that is born King of the Jews?' for we have seen his star in the east, and are come to worship him."

This account adds, after the wise men face King Herod: "When they had heard the king, they departed; and, lo, the star, which they saw in the east, went before them, till it came and stood over where the young child was."

A key reference in Nicholl's book is found in a 1st century letter from St. Ignatius to believers in Ephesus: "A star shown in heaven [with a brightness] beyond all the stars; it's light was indescribable, and its newness provided astonishment. And all the other stars, together with the Sun and the Moon, formed a chorus to the star, yet its light far exceeded them all. And there was perplexity regarding from where this new entity came from, so unlike everything else [in the heavens] was it."

What was this? The 1959 movie "Ben-Hur" featured a star with a giant halo that miraculously crosses the night sky. "The Nativity Story" in 2006 showed Jupiter and Venus aligning with the star Regulus, in the constellation Leo. Other theories have focused on supernova, comets or an appearance by an angel.

Nicholl, whose doctorate is from Cambridge University, based much of his research on Revelation, chapter 12, a text containing images that would be familiar to any astronomer, ancient or modern.

"And there appeared a great wonder in heaven; a woman clothed with the sun, and the moon under her feet, and upon her head a crown of twelve stars," it states. This woman is threatened by a dragon as she gives birth to a "man child, who was to rule all nations with a rod of iron: and her child was caught up unto God, and to his throne."

The only "zodiacal female is Virgo the Virgin," noted Nicholl, and immediately south of her is the constellation figure Hydra, a multi-headed dragon.

Working with cooperative astronomers, Nicholl set out to chart the path of a great comet -- one making close passes by the Sun and Planet Earth -- that would fit into both the biblical narrative and what astronomers know about comets.

The result, he said, would have been a drama in the heavens containing specific symbols and information that would inspire the Magi to begin their journey, ending with them seeing a bright comet tail on the horizon that would point to a site in Bethlehem.

In his book, Nicholl concludes that the divine "plan for the messianic sign was already in motion at the point that the solar system came into existence, and the precise moment of the Messiah's birth was firmly established then, guaranteed by the laws of physics."

The goal from the start was to "take the star of Bethlehem seriously, in terms of what we see in the scriptures," he explained. "This is an example of science and religious scholarship working together to shed light on one of the greatest mysteries, ever."